Just finished up the germanium boost, went very smoothly and seems to work flawlessly. I felt the bias pot needed to be turned all the way up, otherwise it sounded really farty to me, almost like speaker distortion.

I'm pretty happy with it, sort of feel that it's either on or off in the touch sensitivity department though - you really have to dig in to get it to break up unless you have it turned all the way up. Curious if anyone knows any good mods for this pedal to change up the sound, maybe reduce some of the fatness? I'd be willing to try any tweaks for fun.

If you have to run the trimpot at the extreme end of its sweep to get the tone you like best, you may benefit by replacing it with one of greater resistance range, i.e. a 250K. Dialing in a bit more resistance could improve the tone further. These NOS germanium transistors vary widely and some need more resistance than others to bias correctly.

If you have to run the trimpot at the extreme end of its sweep to get the tone you like best, you may benefit by replacing it with one of greater resistance range, i.e. a 250K. Dialing in a bit more resistance could improve the tone further. These NOS germanium transistors vary widely and some need more resistance than others to bias correctly.

You can always pick up another germanium transistor or two online. I would suggest dealing with a reputable seller who pre-tests their trannies, since the supply of good (i.e. reasonable gain and low current leakage) NOS germanium transistors continues to dwindle, though I have heard reports of some new production starting up recently. I'd stay off of eBay for these, since I've heard a lot of horror stories of bad product being passed as good. For reliable NOS Ge trannies, I'd recommend Small Bear.

If you have to run the trimpot at the extreme end of its sweep to get the tone you like best, you may benefit by replacing it with one of greater resistance range, i.e. a 250K. Dialing in a bit more resistance could improve the tone further. These NOS germanium transistors vary widely and some need more resistance than others to bias correctly.

So I removed the 100k trimpot and installed a 250k and I noticed that I'm able to dial it in way grittier with this one if I dime the trimpot and when I back it off, I seem to find a happier medium. I also bought a 500k to potentially try in the future, but I was curious if you could explain what exactly I'm doing to the circuit when I go from a 100k to 250k to 500k trimpot for example? Is this cutting and boosting the current to the germanium transistor?

I'm no theoretician when it comes to how transistors work, but it has to do with getting the bias voltage at the collector of the transistor within a certain range. Somewhere around 7.0VDC (assuming a 9.0VDC power source) is where the effect sounds best to most ears. The issue with achieving this bias voltage is that old production germanium transistors tend to be extremely variable, and the best ones have often been "cherry-picked" out of remaining stocks. So there is often a wide range of gain and current leakage found in these transistors, which affects how they bias. Consequently, you will sometimes need more resistance from the trimpot than the standard 100K version gives. At least, that's how I understand it. Perhaps someone with a stronger theoretical understanding can explain this in more depth....or correct me if I got anything wrong!

I'm no theoretician when it comes to how transistors work, but it has to do with getting the bias voltage at the collector of the transistor within a certain range. Somewhere around 7.0VDC (assuming a 9.0VDC power source) is where the effect sounds best to most ears. The issue with achieving this bias voltage is that old production germanium transistors tend to be extremely variable, and the best ones have often been "cherry-picked" out of remaining stocks. So there is often a wide range of gain and current leakage found in these transistors, which affects how they bias. Consequently, you will sometimes need more resistance from the trimpot than the standard 100K version gives. At least, that's how I understand it. Perhaps someone with a stronger theoretical understanding can explain this in more depth....or correct me if I got anything wrong!

Thanks, that makes sense but definitely open to anyone who has anymore info. Sounds like it might even be worth trying the 500k trim pot, shame their a bit of a pain to remove and replace.

Nothing to be embarrassed about--we all need to learn new things sometimes. Heck, I didn't learn how to use one until I started building pedals when I was nearly 56! Who says you can't teach an old dog new tricks???

For this particular test, you need to be able to measure DC voltage at a test point--in this case, the collector of the germanium transistor. Refer to the image below of the multimeter that BYOC sells. Here's what to do:

Power up the pedal with the rear cover removed. Remember that you need to have a cable inserted in the input jack for the circuit to be energized. Prepare your multimeter by inserting the black probe plug into the COM port and the red one into the port immediately above it. Turn the meter on and set the selector to 20 on the DCV scale. Ground the black probe by inserting it into one of the corner screw bosses of the enclosure--now you're ready to take a measurement. Touch the red probe to the collector of the transistor--that's the leg closest to the edge of the PCB, adjacent to the eyelet labeled "OUT". Hold it there for a few seconds until you get a stable reading (it's fine if it fluctuates by a few hundredths of a volt). That's all there is to it. If it's more than a few tenths of a volt away from 7.0V, adjust the trimpot while holding the probe in contact with the collector until you get it into that range. But also keep in mind that the final judge of the correct setting should be what sounds good to your ear...

Awesome! The mulit-meter supplied to me was a bit different, but I got it working. So I measured the ranges and when I have the bias pot (250k trimpot) turned all the way down it reads 0.05 when I turn it all the way up it reads 6.35 and the sound I felt was the best by my ear was 4.75. This is using a 9V Fulltone noiseless wall-wort power supply (not switching).

This is fascinating any thoughts, it gets really gritty and almost fuzz like when I dime it to what turned out to be 6.35, which is why I had backed it off a more over-drive like 4.75.

Sounds to me like you've just got a germanium transistor that needs a lot of resistance to bias correctly. Nominal for the classic Rangemaster treble booster circuit is a fixed resistor of 68K. You're up to nearly 4 times that resistance and the collector is just getting into the "nominal" voltage range. But if it's sounding good to you around 4.75V, that's what to go by.

The Texas, the Newmarket, or anything in the middle row should do the job. You don't want any of the NPN trannies or the ones sold in pairs, since they are for different versions of the pedal than you have.

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